Electrophotographic recorder



Jan. 10, 1956 H. G. @REIG ELECTROPHOTOGRAPHIC RECORDER 5 Sheets-Sheet l Filed NOV. 26, 1951 3 Sheets-Sheet 2 Filed Nov. 26, 1951 Jan. 10, 1956 H, G, @REIG 2,730,023

ELECTROPHOTOGRAPHIC RECORDER al w I'f@ l 'Il' w 1"mmf"l, im m INVENTOR United States Patent JO ELEcrRoPHoroGRAPmc RECORDER Harold G. Greig, Princeton, N. J., assigner to Radio Corporation of America, a corporation 'of Delaware Application November 26, 1951, Serial No. 258,145 8 claims. (ci. 9s-1.7)

The present invention relates to an electrostatic'printer or printers employing electrophotogra'phy, and more par ticularly, althought not necessarily exclusively,"to means in a continuous electrostatic printer forfveeding developer material in a`nove1 manner'over a light rsensitive photoconductive surface. y

The invention is embodied illustratively in an electrophotographic printer having a moving endless charge receiving surface which is continuously exposed to electrostatic charging means. A light image, of letter type, for example, is produced and projected on the endless charged surface'either intermittently, for example a line of Vtype at a time, or continuously by the production of successive elementary image strips. The moving surface, following exposure to the light image, however it may'be'applied, is subjected to a continuously maintained and preferably transverse ow of developer mix. The nature of the developer mix will -be more fully described hereinafter for the sake of completeness of disclosure, although it is not part of the present invention. The llow of developer mix develops a latent image for transfer' to the usurface of a web or sheet. The charged moving'suface bearing the developed or power image, a succession of such images, or successive parts of one such image is contacted in the presence of a member Vor members providing an electric charge by a web or sheet, of treated or 'untreated paper, or the like which receives the charge. Close interfacial contact between the charge receiving surface and the web or sheet is insured by the charge at the former surface. The contact'between'the web andthe charge receiving surface need be maintained over a relatively short linear distance of the latter. The light sensitive photoconductive charge receiving surface is vrnext subjected lto a cleaning operation thereby to remove any remaining developer.

In accordance with the present invention, the quantity or bulk of the developer `mix may be maintained below an excessive value to avoid loss of the latent image in a recorder embodying the present invention. Also, the rate of iiow of developer m-ix may be controlled Within suitable limits.

The principal object of the .present invention isr to provide novel means for applying a developer mix to a charge receiving surface in a printer for printing by electron photographic or electrostatic printng'metho'ds. i

Another object of the invention is to provide novel means for causing a granular material continuously to transverse an inclined concave surface.

A further object of the invention is to provide a novel arrangement including a plurality'of helices for returning a supply of granular material to a position for reuse,

Other objects and advantages of the invention will, of course, become apparent and immediately suggest themselves to those skilled in the art to which the invention is directed from a reading of the following specicaftion in connection with the accompanying drawings in which;

Fig. l is a view in top, planishowing, iagrarnmat'icall'y, a printer embodying lthe vpresent inven'tii associated 2 With'a cathode ray tube for producing a radiante'nergy or luminous image of subject 'matter to be recorded on a sheet or web of recording material;

Fig. 2 is a view in side elevation of the apparatus shown diagrammatically in Fig. `1;

Fig. 3 is a section, the section being taken on line 3-3 of Fig. l as viewed in the direction of the arrows;

Fig. 4 is a vertical section, the section being taken on line 4 4 of Fig. 3 as viewed in the direction of the arrows.

Referring to the drawing, and for the present, to Figs. l and 2 thereof, reference character 10 designates the illustrative embodiment of the printer of this invention in its entirety. The printer 10 includes ymechanical driving means, the principal part of which is the shaft 12. Driving power is imparted tothe shaft 12 from a motor 14 through pulleys 16 and 18 and a belt 19. The motor-14 may be of variable'speed type or the belt'and pulley arrangement may be replaced or preceded in the driving system by a suitable vvariable speed gear drive (not shown). The motor 14 should be capable of maintaining any selected operating speed'reasonably constant.

The printer 10 has a iixing means such,'for example, as the electrical or other type of heater V22 associated with it. The heater 2 2 may be included in 'the structure of the printer. The printer 10 also includes a suitably supported recording web driving and guiding mechanism indicated generally by reference character 24.

As will appear hereinafter, the photoconductive surface of the printer lll is'so arranged that a luminous image may be projected thereon in 'a direction initially extending parallel 'to the axis of the printer.. The photoconductive surface is cylindrical and, in the illustrative example, is presentedl by the interior surface 25`of a cylindrical member 27. In the arrangement of Figs. l and 2, the luminous image to be recorded is produced by a cathode ray tube 26 which is mounted ina suitable protective shielding housing 28. A lens system 31 serves'to project the image appearing on the face of4 the cathode ray tube onto the photoconductive surface of the receiver. The printer 1i),- including the web driving and guiding means 24, is mounted on a base 33. This base provides a convenient support aiso for the housing 28 and the lens system 31. The base 33 is inclined to the horizontal when the printer 10 isin use as indicated by the angle made by the base with'a horizontal dashed line 3d. The horizontal line 34 may represent a bench, table, or other support for the printer 10. i

The cathode ray tube lois provided with the usual appliances as will be understood-bythose skilled in the art to provide vdeflection of ythe cathode ray beam therein. This beam Will'be-modulated by signals similar to video signals. Only horiaontal deliection means may be provided in which case'the second coordinate of dedection will be provided by movement of the light `sensitive or charge receiving surface 25 of the recorder. The cathode ray tube 26 may be operated soas to produce characters similar to typewri'tten characters arranged in a horizontal row with a plurality of characters being formed successively. Theformation of the row `of characters is cyclically 'repeated with the same or different lcharacters produced. The arrangement for producing a scanning line or an imageof any desired -type on the'face of the cathode ray tube is not part of tl'ie present invention and need not be further disclosed herein. An arrangement for successively producing type characters arranged in a row is shown in the copending application' of Warren H. Bliss, Serial No. 213,389, tiled March l, 19'51. As disclosed in that application, 32 letters, for example, may be traced successively, in a horizontal row by deflection of the cathode `ray beam in Ythe tube 26. Thesev 32 letters are or may b'e produced in JA@ ofase'cnd. The peripheral Speed of 'the charge'receiving sirfce yof tle recorder 10 is or may be such that its displacement is equivalent to the height of one line of type produced on the face of the cathode ray tube in 1A@ of a second. These figures are given by way of example only, and it will be understood that any luminous image, however produced, may be recorded by the recorder 10.

The recorder comprises stationary end plates 38 and 39. The end plates 38 and 39 are united into a rigid structure and are spaced apart by a number of tie rods 42, for example three (Fig. 3). Screws 43 serve to clamp the end plates against ends of the rods 42. The end plates assembled with the rods 42 may rest upon or be secured to the base 33.

A pair of rollers 48 (Fig. 2), each having a flange 49, receives the end plates 51 and 52 of the supporting arrangement for the cylindrical member 27. A pair of rollers 61, each having a ange 63, also receives the end plates 51 and 52. The rollers 48 in combination with the angularly displaced rollers 61 serve as a cradle upon which the cylindrical structure comprising the member 27 rotates.

The end plates 51 and 52 of the rotatable supporting structure for the cylindrical member 27 are joined by strips 70, 71, and 72 of sheet metal or the like. Each strip is turned upwardly at each end as indicated at 74. The ends 74 are engaged in radial grooves 76 in the plates 51 and 52 and are secured by screws 78. Each end plate has a circular groove 81 and a cylindrical member 83 formed of a transparent plastic sheet is engaged at its ends in the circular grooves. A circular sheet metal ring 86 is engaged in the groove 81 in the plate 51 to seive as a reinforcement for the cylindrical member 83. A similar metal ring 88 is engaged in the groove 81 in the end plate 52. The cylindrical member 83 is preferably, but not necessarily, made of transparent material. The cylindrical member 83, if transparent, permits observation of circulation of the developer mix.

The previously mentioned cylindrical member 27 is spaced from the circular member 83 by a plurality of helically arranged strips 89. In the illustrative example, fourteen strips 89 are provided which may be secured to the cylindrical member 27 by any suitable means, such as by cementing, to form a plurality of channels as hereinafter set forth. The strips 89 extend beyond the edge of the member 27 on the side of the rotatable device bounded by the end plate 51. This extension may be approximately l inch, for example. The ends of the strips 89 stop short of the edge of the cylindrical member 27 adjacent the end plate 52. For example, the strips may extend to within one-half inch of the edge of the cylindrical member 27.

The cylindrical member 27 is a metal cylinder the inside surface 25 of which is polished and coated with a photoconductive material such, for example, as selenium. Aluminum is a suitable material. The selenium coating is, or may be, applied by evaporation at reduced pressure.

The several appliances for obtaining the record on a paper web as well as the web reel and the guide for the web are carried by the end plates 38 and 39 in such a way that their position may be circumferentially adjusted about the interior of the photosensitive surface 25. The end plate 39 is recessed as indicated at 92 which is covered by a ring 94 to provide a circular groove 98. The ring 94 is secured to the end plate 39 by means of screws 96. The plate 38 is mso recessed to provide a groove 95 in conjunction with a ring 99 similar to the ring 94. ln the illustrative example of a printer involving the present invention, the cylindrical member 27 is rotatable in a counter-clockwise direction as viewed in Fig. 4 of the drawing.

The appliances associated with the photoconductive surface will be described in the order in which they cooperate with said surface beginning with the arrangement for cleaning the surface of excess developer mix or powder remaining following take off on the paper web of the characters to be recorded. Reference character 102 indicates a channel shaped member, the open side of which is spaced slightly from the photosensitive surface 25. The interior of this channel shaped member 102 is in communication with a conduit 103 which may be connected to any suction line or suction device such as, for example, a vacuum cleaner.

The surface 25 is charged to a high positive potential in the illustrative machine 10 by a plurality of wires 108. These wires may, for example, be three in number and may be spaced TA6 inch from the selenium surface. A bar member 112, provided with angularly turned ends seated in the grooves and 98, carries insulating wire holders 118 between which the wires 108 are stretched. The wires 108 are connected to a 6.5 kv. source of positive potential, for example. A grid of wires 124 is stretched between insulating wire holders 125. The latter are also secured to the bar member 112. ln the illustrative example, nineteen wires 124 are provided which are spaced 1A; inch apart and grounded to the frame of the machine. The central portion of this grid of wires is S/g inch from the selenium surface. The dimensions are given solely by way of example.

As previously described, the image on the cathode ray tube 26 is projected on the selenium surface 25 by the lens system 31. This is accomplished by a mirror 131 which is inclined as shown with respect to the axis of the machine 10 to project the image from the cathode ray tube face, or other image source, onto the surface 25 following exposure to the high positive potential applied by the wires 108. The image, so projected, is located axially along the surface 25. The mirror 131 is secured in any suitable manner to a metal or other sufficiently rigid strip 132. This strip is bent so as to provide radially extending ends 136 which are received in the grooves 95 and 98.

A quantity of developer is placed in the cylindrical member 27 and this powder ows axially along the surface 25. The path of powder flow is angularly displaced counter-clockwise from the line or lines of impingement of the image projected by the mirror 131 as viewed on Fig. 4 of the drawing. Suitable developers for xerography use are known and it will be understood that the machine 10 can be used with any suitable powder having predetermined triboelectric properties. A form of developer giving excellent results in the machine 10 is made up of glass beads and sulphur particles coated with coprecipitated organic coloring matter. The coloring matter is, for example, spirit soluble nigrosine and spirit soluble Iosol Black. The glass beads are negative with respect to the sulphur coated with the coprecipitated coloring matter. The latter takes a positive charge. The developer powder briefly described herein as giving excellent printing results is fully disclosed in a copending application for Letters Patent of Harold G. Greig, Serial No. 187,827, tiled September 30, 1950, and entitled Improvement in Electrostatic Printing.

In the illustrative machine 10, the quantity of developer is circulated by the helical strips 89 as the cylinder rotates. The surplus developer after traversing the surface 25 may be collected in a second hopper after being discharged by gravity from the lower end of the cylinder.

The projecting ends of the strips opposite the end plate 38, as they continuously pass the lowest point of the rotating cylinder, scoop up or trap a quantity of the developer powder which rests by gravity in the lowermost part of the cylinder. It will be understood that as the cylinder rotates, the powder will flow at a controlled rate axially along the cylinder and that the path of flow will be displaced to the right of the axial plane of the cylinder as it is viewed in Fig. 4 of the drawing. This feature of a machine embodying the present invention provides some additional angular spacing between the wires 108 and the point of impingement of the luminous image on the-surface 25. 'It fwillbe understood that as the cylinder rotates,.thedeveloper `which is trapped in the channels between the strips 89 will be discharged from these channels, and that the excess or overflow, which is continuously transferred to thebotto'm of the cylinder, will iiow across the cylindrical member. It willbe noted that the strips 89 ldo not extend for the full length of the cylinder 27 to the left as viewed in'Fig. 3. This permits smoother flow of the accumulated Vpowder onto the inner selenium surface 25.

The paper web, designated by reference character 141, is fed from a roll 143. This roll is conveniently mounted on a spindle 146 supported by brackets 148 and 149. A helical spring 151, bearing against a disc 152, assists in centering the roll by biasing it into contact with a second disc 153. The web 141, as it feeds from the roll 143, passes under a rod 161 so that it is substantially in contact with the surface 25. The web is held against the surface 25 by the electrostatic charge from the transfer unit and is peeled from the surface at the point where it passes over a second rod 166. The rod 166 is carried by a bracket 16S which is received in the groove 95. The other end of this rod is carried by a second bracket 169 received in the groove 98. A second rod 173 extends diagonally across the machine substantially in the horizontal plane of the rod 166. The rod 173 is supported at one end by the bracket 169 and at its other end by a bracket 176. The bracket 176 is received in the groove 98. After passing over the rod 166, the paper web also passes over the rod 173 and passes from beneath this last named rod to an inclined rod 179 (Fig. 1). The rod 179 forms part of the previously mentioned web driving and guiding means 24. The previously mentioned power shaft 12 drives a roll 182 through the belt and pully connections 183. The driven roll 182, along with an idler roll 186, forms a pair of driving pinch rollers through which the web is passed after being turned over the top of the inclined rod 179.

The transfer unit as shown in Fig. 3 comprises the previously mentioned insulating member 163 carried by brackets 188 and 189, received in the grooves 95 and 98. The member 163 is pierced at intervals to receive pointed electrodes such as needles 192 which project toward the portion of the web 141 in contact with the surface 25. A connection to each of the needles 192 from a suitable high voltage source (not shown) is made by a conductor 196. Th outer ends of the needles are protected by a corona shield 197.

l claim:

l. An electrophotographic recorder comprising an imperforate hollow cylinder, means to impart rotation to said cylinder, a second imperforate hollow cylinder nested within said first/named cylinder, said second cylinder having a photoconductive inner surface, means for spacing said second named cylinder substantially coaxially with said iirst named cylinder, said last named means providing one or more helical passageways between said first named and said second named cylinders extending substantially from end to end axially of said cylinders.

2. An electrophotographic recorder comprising an imperforate hollow cylinder, flanges at each end of said member, rotatable rollers for receiving said flanges to support said cylinder and to impart rotation thereto, a second imperforate hollow cylinder nested within said first named cylinder, said second cylinder having a photoconductive inner surface, means for spacing said second named cylinder substantially coaxially with said first named cylinder, said last named means providing one or more helical passageways between said first named and said second named cylinders extending substantially from end to end axially of said cylinders.

3. An electrophotographic recorder comprising an irnperforate hollow member, means to impart rotation to said cylinder, a second imperforate hollow cylinder nested within said first named cylinder, said second cylinder havinga photoconductive inner surface,"mean'sfor'spacing said second named cylinder substantially 'coaxiallyfwith said first named cylinder, said last named meanscomprising helically disposed strips toprovide one or more helicalpassageways between 'said-rst named and said second named cylinders extending substantially from end to end y axiallyof said cylinders.

4. An electrophotographic recorder comprising an irnpe'rfor'ate hollow cylinder, means providing ay partial closurefor each end of said cylinder whereby to contain a quantity of iiuent material, means to impart'rotatio'n to saidcylinder, a second imperforate hollow cylinder nested within said -iirst named cylinder, said second cylinder having aphotocondu'cltiveinner'surface, meansafor spacing said second named cylinder substantially coaxially with said iirst named cylinder, said last named means providing one or more helical passageways between said first named and said second named cylinders extending substantially from end to end axially of said cylinders whereby to cause iiuent material to be returned from one end to the other of said cylinders.

5. An electrophotographic recorder comprising an imperforate hollow cylinder, means providing a partial closure for each end of said cylinder whereby to contain a quantity of fluent material, means to support said cylinder with its axis inclined to the horizontal, a second imperforate hollow cylinder nested within said rst named cylinder, said second cylinder having a photoconductive inner surface, means for spacing said second named cylinder substantially coaxially with said tirst named cylinder, said last named means providing one or more helical passageways between said rst named and said second named cylinders extending substantially from end to end axially of said cylinders whereby to cause fluent material to be returned from one end to the other end of said cylinders.

6. An electrophotographic recorder comprising an imperforate hollow cylinder, means providing a partial closure for each end of said cylinder whereby to contain a quantity of fluent material, means to support said cylinder with its axis inclined to the horizontal, a second imperforate hollow cylinder nested within said lirst named cylinder, said second cylinder having a photoconductive surface, a plurality of helically disposed strips for spacing said second named cylinder substantially coaxially with said first named cylinder, said strips being spaced to provide a plurality of helical passageways between said first named and said second named cylinders extending substantially from end to end axially of said cylinders whereby to cause liuent material to be returned from one end to the other of said cylinders.

7. An electrophotographic recorder comprising a transparent cylindrical member, a liange at each end of said cylindrical member providing a partial closure for each end of said cylindrical member whereby to contain a quantity of iiuent material, means to support said cylindrical member with its axis inclined to the horizontal, means to impart rotation to said inclined cylindrical member, a second cylindrical member nested within said first named cylindrical member, the interior surface of said second cylindrical member being photoconductive, a plurality of helically disposed strips for spacing said second named cylindrical member substantially coaxially with said first named cylindrical member, said strips being spaced to provide a plurality of helical passageways between said iirst named and said second named cylindrical members extending substantially from end to end axially of said cylindrical members whereby to cause fluent material to be returned from one end to the other of said cylindrical members.

8. An electrophotographic recorder comprising a cylindrical member, means providing a partial closure for each end of said cylindrical member whereby to contain a quantity of iiuent material, means to support said cylindrical member with its axis inclined to the horizontal, means to impart rotation to said inclined cylindrical member, a second and axially shorter cylindrical member nested within said rst named cylindrical member, a plurality of helically disposed strips for spacing said second named cylindrical member substantially coaxially with said rst named cylindrical member, said strips extending beyond the end of said second cylindrical member at the lower end thereof and ending short of the higher end, said strips being spaced to provide a plurality of helical passageways between said first named and said second named cylindrical members extending substantially from end to end axially of said cylindrical members whereby to cause uent material to be returned from one end to the other of said cylindrical members.

References Cited in the le of this patent UNITED STATES PATENTS Hamilton Sept. 9, Fatscher et al Mar. 6, Wildhaber May 28, Rich July 8, Hunter Jan. 5, Wynd Apr. 4, Carlson Ian. 6, 

